I wonder how many people that would actually affect? All iPhones that support iOS 18 support eSIM. Starting with iPhone 14 all iPhones except the SE have only had eSIM.

I would guess that most people with only one SIM go with eSIM if they phone supports it.

You can put a PIN on an eSIM, but is there really much point? My understanding is that the main point of a SIM PIN is so that someone cannot transfer your physical SIM to another phone.

Without a PIN someone could steal your phone and even if they could not get past the phone lock they could just move the physical SIM to their phone and thus take over your phone number. They don't even need to steal your phone--they just need access to it for a few seconds to remove the SIM.

That's not the case with eSIM.

You might want a PIN to keep others from making/receiving calls if they have access to your unlocked phone, but because SIMs permanently lock after 3 failed unlock attempts (with no timeout--a mistake today, another a year from now, and another two years after that and it locks) that's probably asking for trouble.